SMN1 and amyotrophic lateral sclerosis: Intrinsic motor neuron defects and non-cell autonomous toxicities in associated cell types (e.g., glia, interneurons) contribute to ALS (Ilieva et al., 2009; Ramírez-Jarquín et al., 2014; Puentes et al., 2016), but similar to SMA, the exact mechanisms underpinning motor neuron death, and their relative vulnerability-resistance axis (Nijssen et al., 2017), remain to be elucidated.